Add workflow for publishing on crates.io

The workflow triggers on tag pushes, and must be approved by an organization
member with push access. Once approved, the workflow will try publishing the
crates in the correct order to crates.io

Author: toasteater

.github/workflows/publish.yml

@@ -0,0 +1,40 @@
+name: Publish to crates.io
+
+on:
+  push:
+    branches:
+      - '!*'
+    tags:
+      - '*'
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    environment: Deploy
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@b2417cde72dcf67f306c0ae8e0828a81bf0b189f
+        with:
+          profile: minimal
+          toolchain: stable
+          components: rustfmt, clippy
+      - name: Sanity tests
+        run: |
+          cargo fmt --all -- --check;
+          cargo clippy --all --all-features -- -D clippy::style -D clippy::complexity -D clippy::perf -D clippy::dbg_macro -D clippy::todo -D clippy::unimplemented;
+          cargo test --all --all-features;
+      - name: Publishing to crates.io
+        env:
+          CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_TOKEN }}
+        run: |
+          (cd impl/proc_macros && cargo publish);
+          (cd gdnative-sys && cargo publish);
+          (cd gdnative-derive && cargo publish);
+          (cd gdnative-core && cargo publish);
+          (cd bindings_generator && cargo publish);
+          (cd gdnative-bindings && cargo publish);
+          (cd gdnative && cargo publish);